Developer John Hindmarsh, of the Hindmarsh construction company, said once paid parking reached $15 a day in Canberra, it would become tempting to build an above-ground car park.

Multistorey underground car parks were more expensive to build and would become a realistic option for developers once parking costs reached $20 a day, Mr Hindmarsh said.

With public servants about to be hit with $11-a-day parking costs in the triangle from July 1, that threshold may not take too long to reach.

Mr Hindmarsh said his ideal spot for an underground car park near the triangle would be off London Circuit in Civic, close to the Canberra Theatre.

''We would certainly look at it if the government decided to put it out to commercial development,'' he said. ''At the moment, they are looking after it themselves.''

Property Council of Australia executive director Catherine Carter said forcing public servants to pay for parking would deliver a lot of benefits to a wide area.

''For many years the Property Council has been strongly lobbying for paid parking in the parliamentary zone, and there are a lot of reasons for that,'' she said. ''Car parking being free for public servants in Russell Hill and Barton car parks creates problems.''

Ms Carter explained: ''A lot of people get in early and park to go to work, displacing car parking for other visitors.

''The national cultural institutions have really suffered because while public servants park there, it means people who are wanting to visit the galleries cannot park and get in to visit. And workers in Civic who don't want to pay will park in Russell and Barton and take the 10-minute walk across the bridge, so they also absorb all the car parking to the detriment of visitors.

''When parking is free in major car parks in the city, it has knock-on effects. It means developers are reluctant to go into paid car parking, which perversely means there's less parking because it's not a commercial proposition for a developer to build one.''